Cephamycin

Cephamycin is a subclass of beta-lactam antibiotics within the cephalosporin family. It is defined by a structural modification of the cephem nucleus, notably a 7α-methoxy group, which confers greater resistance to certain beta-lactamases and enhances activity against anaerobic bacteria. Typical members include cefoxitin, cefotetan, cefmetazole, and related agents such as flomoxef.

The spectrum of cephamycins includes activity against many Gram-negative bacilli and strong coverage of anaerobes, particularly Bacteroides fragilis. They generally show limited activity against Pseudomonas aeruginosa and many nonfermenters and have only moderate activity against some Gram-positive cocci. Resistance is largely due to beta-lactamases such as ESBLs and AmpC enzymes that can hydrolyze cephamycins, reducing their usefulness against certain Gram-negative pathogens.

Mode of action follows the classical beta-lactam mechanism: inhibition of cell wall synthesis by binding to penicillin-binding proteins, resulting in bactericidal activity. Most cephamycins are administered parenterally (intravenous or intramuscular) and have variable oral bioavailability. Pharmacokinetics vary by agent, but many are excreted renally with some biliary excretion.

Clinical uses include prophylaxis in abdominal and gynecologic surgeries to cover anaerobes and mixed flora, and treatment of intra-abdominal or pelvic infections where anaerobic coverage is desirable. They are not reliable for Pseudomonas infections and are not first-line agents for MRSA or many resistant Gram-negative pathogens.

Adverse effects are similar to other beta-lactams and may include hypersensitivity reactions, diarrhea, and rash. Some cephamycins carrying a methylthio tetrazole (MTT) side chain, such as cefotetan and cefmetazole, can cause coagulopathy and, in certain cases, disulfiram-like reactions with alcohol.